Isothermal crystallisation of end-linked poly(tetrahydrofuran) networks. 3. Small-angle neutron scattering

The crystallisation kinetics of the end-linked poly(tetrahydrofuran) (PTHF) network has been investigated in terms of small-angle neutron scattering (SANS). Fully deuterated PTHF (DPTHF, D) and hydrogenated PTHF (HPTHF, H), having degrees of polymerisation, N_D=166 and N_H=142, respectively, were blended before cross-linking. Two types of labeled network, one 5% and the other 50% hydrogenously labeled, were employed, where the major component was designed to be deuterated polymers in order to minimise the incoherent scattering. In the molten state (T=50°C), the structure factors for both network and linear polymer blend are well described with the de Gennes' scattering intensity function for polymer blends. On the other hand, a significant domain scattering due to the presence of crystalline lamellar structure was observed in the solid state (T=20°C for crystallisation time=∞). During isothermal crystallisation, initiated by quenching the network film from 60 to 20°C, the radius of gyration of the labeled chain and the apparent interaction parameter, χ_app, increased slightly with time. This indicates that a crystallisation leads to miscibility reduction of the amorphous region. A scattering maximum, q_m, corresponding to the lamellar identity period, appeared and increased with time. The crystallisation for the network was found to be considerably slower than that of the corresponding linear polymer blends. These results were consistent with those obtained by small-angle X-ray scattering on the same system.